Voltage/current regulator improvements for an implantable medical device

ABSTRACT

Apparatus and method provide flexibility in generating a stimulation waveform to an electrode of an implantable medical device. The stimulation waveform comprises at least one stimulation pulse. The embodiment of the invention supports a generation of a stimulation pulse in which an amplitude and an electrical polarity of the stimulation pulse can be dynamically changed. The embodiment comprises a capacitor arrangement, a regulator and a switching array. The capacitor arrangement can be reconfigured with respect to an electrical reference through the switching array in order for the regulator to deliver the stimulation pulse to a pair of electrodes. In another embodiment, a plurality of stimulation waveforms are generated in which different stimulation waveforms are associated with different electrodes. With the embodiment, a plurality of regulators are connected and reconfigured to the capacitor arrangement in order that the different stimulation waveforms are generated by different regulators.

FIELD OF THE INVENTION

[0001] This invention relates generally to implantable medical devices,and more particularly to the generation of stimulation pulses forimplantable neurological stimulators for purposes of influencing thehuman body.

BACKGROUND OF THE INVENTION

[0002] The medical device industry produces a wide variety of electronicand mechanical devices for treating patient medical conditions.Depending upon medical condition, medical devices can be surgicallyimplanted or connected externally to the patient receiving treatment.Clinicians use medical devices alone or in combination with drugtherapies and surgery to treat patient medical conditions. For somemedical conditions, medical devices provide the best, and sometimes theonly, therapy to restore an individual to a more healthful condition anda fuller life. One type of implantable medical device that can be usedis an Implantable Neuro Stimulator (INS).

[0003] An INS generates an electrical stimulation signal that is used toinfluence the human nervous system or organs. Electrical contactscarried on the distal end of a lead are placed at the desiredstimulation site such as the spine and the proximal end of the lead isconnected to the INS. The INS is then surgically implanted into anindividual such as into a subcutaneous pocket in the abdomen. The INScan be powered by an internal source such as a battery or by an externalsource such as a radio frequency transmitter. A clinician programs theINS with a therapy using a programmer. The therapy configures parametersof the stimulation signal for the specific patient's therapy. An INS canbe used to treat conditions such as pain, incontinence, movementdisorders such as epilepsy and Parkinson's disease, and sleep apnea.Additional therapies appear promising to treat a variety ofphysiological, psychological, and emotional conditions. As the number ofINS therapies has expanded, greater demands have been placed on the INS.Examples of some INSs and related components are shown and described ina brochure titled Implantable Neurostimulation Systems available fromMedtronic, Inc., Minneapolis, Minn.

[0004] The effectiveness of the therapy as provided by the INS isdependent upon its capability of adjusting the electricalcharacteristics of the stimulation signal. For example, stimulationwaveforms can be designed for selective electrical stimulation of thenervous system. Two types of selectivity may be considered. First, fiberdiameter selectivity refers to the ability to activate one group ofnerve fibers having a common diameter without activating nerve fibershaving different diameters. Second, spatial selectivity refers to theability to activate nerve fibers in a localized region withoutactivating nerve fibers in neighboring regions.

[0005] The tissue around a first stimulated electrode can be damaged bya charge accumulation as a result of electrical stimulation. Thus, arecharging interval is typically utilized to balance a chargeaccumulation that may occur around the surrounding tissue of the firststimulated electrode. Typically an implantable medical device (such asan implantable neurological device), utilizes a passive rechargeinterval to balance the accumulated charge. The passive rechargeinterval can be increased in order to better balance the charge.However, a stimulation pulse may be delayed as a result of increasingthe passive recharge interval. Moreover, a stimulation pulse may be usedto pre-condition a main stimulation pulse.

[0006] The above observations may require the clinician to consider anumber of factors such as the type of disorder and the specificcondition of the patient in order to determine the electricalcharacteristics of the stimulation signal. Apparatus and method thatprovide flexibility in adjusting the electrical characteristics of thestimulation signal (such as an amplitude and electrical polarity of astimulation pulse) in order to improve the effectiveness of treatmentand to facilitate the clinician's task is beneficial to the field ofImplantable Neuro Stimulators.

BRIEF SUMMARY OF THE INVENTION

[0007] In the embodiment of the invention, apparatus and method provideflexibility in generating a stimulation waveform to an electrode of animplantable medical device such as an Implantable Neuro Stimulator(INS). The stimulation waveform comprises at least one stimulationpulse. The embodiment of the invention supports a generation of astimulation pulse in which an amplitude and an electrical polarity ofthe stimulation pulse can be dynamically changed. The embodimentcomprises a capacitor arrangement, a regulator and a switching array.With the embodiment, the capacitor arrangement can be reconfigured withrespect to an electrical reference through the switching array in orderfor the regulator to deliver the stimulation pulse to a pair ofelectrodes.

[0008] In another embodiment, a plurality of stimulation waveforms aregenerated in which different stimulation waveforms are associated withdifferent electrodes. With the embodiment, a plurality of regulators areconnected and reconfigured to the capacitor arrangement in order thatthe different stimulation waveforms are generated by differentregulators.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows an environment of an exemplary Implantable NeuroStimulator (INS);

[0010]FIG. 2 shows an INS block diagram;

[0011]FIG. 3 shows an INS basic operation flowchart;

[0012]FIG. 4 shows a telemetry module block diagram;

[0013]FIG. 5 shows a telemetry operation flowchart;

[0014]FIG. 6 shows a recharge module block diagram;

[0015]FIG. 7 shows a recharge module operation flowchart;

[0016]FIG. 8 shows a power module block diagram;

[0017]FIG. 9 shows power module operation flowchart;

[0018]FIG. 10 shows a therapy module block diagram;

[0019]FIG. 11 shows a therapy module operation flowchart;

[0020]FIG. 12 shows a therapy measurement module block diagram;

[0021]FIG. 13 shows a therapy measurement module operation flowchart;

[0022]FIG. 14 shows a stimulation engine system according to anembodiment of the present invention;

[0023]FIG. 15A shows a logic flow diagram for detecting anout-of-regulator condition according to an embodiment of the presentinvention;

[0024]FIG. 15B shows an electrical configuration corresponding to aregulator according to an embodiment of the present invention;

[0025]FIG. 16 shows a logic flow diagram for detecting a faulty couplingcapacitor according to an embodiment of the present invention;

[0026]FIG. 17 shows a first configuration for a set of regulatorsaccording to an embodiment of the present invention;

[0027]FIG. 18 shows a second configuration for a set of regulatorsaccording to an embodiment of the present invention;

[0028]FIG. 19 shows a stimulation waveform according to an embodiment ofthe present invention;

[0029]FIG. 20 shows a state diagram for a finite state machine to formthe stimulation waveform as shown in FIG. 19 according to an embodimentof the present invention;

[0030]FIG. 21 shows wave shaping of a stimulation pulse shown in FIG. 19according to an embodiment of the present invention;

[0031]FIG. 22 shows a first apparatus that supports wave shaping asshown in FIG. 21 according to an embodiment of the present invention;

[0032]FIG. 23 shows a second apparatus that supports wave shaping asshown in FIG. 21 according to an embodiment of the present invention;

[0033]FIG. 24 shows a logic flow diagram representing a method forsupporting wave shaping according to an embodiment of the presentinvention;

[0034]FIG. 25 shows a stimulation arrangement according to prior art;and

[0035]FIG. 26 shows a stimulation arrangement according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Overall Implantable Medical Device System. FIG. 1 shows thegeneral environment of an Implantable Neuro Stimulator (INS) medicaldevice 14 in accordance with a preferred embodiment of the presentinvention. The neurostimulation system generally includes an INS 14, alead 12, a lead extension 20, an External Neuro Stimulator (ENS) 25, aphysician programmer 30, and a patient programmer 35. The INS 14preferably is a implantable pulse generator that will be available fromMedtronic, Inc. with provisions for multiple pulses occurring eithersimultaneously or with one pulse shifted in time with respect to theother, and having independently varying amplitudes and pulse widths. TheINS 14 contains a power source and electronics to send precise,electrical pulses to the spinal cord, brain, or neural tissue to providethe desired treatment therapy. In the embodiment, INS 14 provideselectrical stimulation by way of pulses although alternative embodimentsmay use other forms of stimulation such as continuous electricalstimulation.

[0037] The lead 12 is a small medical wire with special insulation. Thelead 12 includes one or more insulated electrical conductors with aconnector on the proximal end and electrical contacts on the distal end.Some leads are designed to be inserted into a patient percutaneously,such as the Model 3487A Pisces-Quad® lead available from Medtronic, Inc.of Minneapolis Minn., and some leads are designed to be surgicallyimplanted, such as the Model 3998 Specify® lead also available fromMedtronic. The lead 12 may also be a paddle having a plurality ofelectrodes including, for example, a Medtronic paddle having modelnumber 3587A. Those skilled in the art will appreciate that any varietyof leads may be used to practice the present invention.

[0038] The lead 12 is implanted and positioned to stimulate a specificsite in the spinal cord or the brain. Alternatively, the lead 12 may bepositioned along a peripheral nerve or adjacent neural tissue ganglialike the sympathetic chain or it may be positioned to stimulate muscletissue. The lead 12 contains one or more electrodes (small electricalcontacts) through which electrical stimulation is delivered from the INS14 to the targeted neural tissue. If the spinal cord is to bestimulated, the lead 12 may have electrodes that are epidural,intrathecal or placed into the spinal cord itself. Effective spinal cordstimulation may be achieved by any of these lead placements.

[0039] Although the lead connector can be connected directly to the INS14, typically the lead connector is connected to a lead extension 20which can be either temporary for use with an ENS 25 or permanent foruse with an INS 14. An example of the lead extension 20 is Model 7495available from Medtronic.

[0040] The ENS 25 functions similarly to the INS 14 but is not designedfor implantation. The ENS 25 is used to test the efficacy of stimulationtherapy for the patient before the INS 14 is surgically implanted. Anexample of an ENS 25 is a Model 3625 Screener available from Medtronic.

[0041] The physician programmer 30, also known as a console programmer,uses telemetry to communicate with the implanted INS 14, so a physiciancan program and manage a patient's therapy stored in the INS 14 andtroubleshoot the patient's INS system. An example of a physicianprogrammer 30 is a Model 7432 Console Programmer available fromMedtronic. The patient programmer 35 also uses telemetry to communicatewith the INS 14, so the patient can manage some aspects of her therapyas defined by the physician. An example of a patient programmer 35 is aModel 7434 Itrel® 3 EZ Patient Programmer available from Medtronic.

[0042] Those skilled in the art will appreciate that any number ofexternal programmers, leads, lead extensions, and INSs maybe used topractice the present invention.

[0043] Implantation of an Implantable Neuro Stimulator (INS) typicallybegins with implantation of at least one stimulation lead 12 usuallywhile the patient is under a local anesthetic. The lead 12 can either bepercutaneously or surgically implanted. Once the lead 12 has beenimplanted and positioned, the lead's distal end is typically anchoredinto position to minimize movement of the lead 12 after implantation.The lead's proximal end can be configured to connect to a lead extension20. If a trial screening period is desired, the temporary lead extension20 can be connected to a percutaneous extension with a proximal end thatis external to the body and configured to connect to an External NeuroStimulator (ENS) 25. During the screening period the ENS 25 isprogrammed with a therapy and the therapy is often modified to optimizethe therapy for the patient. Once screening has been completed andefficacy has been established or if screening is not desired, the lead'sproximal end or the lead extension proximal end is connected to the INS14. The INS 14 is programmed with a therapy and then implanted in thebody typically in a subcutaneous pocket at a site selected afterconsidering physician and patient preferences. The INS 14 is implantedsubcutaneously in a human body and is typically implanted near theabdomen of the patient.

[0044] System Components and Component Operation. FIG. 2 shows a blockdiagram of an exemplary INS 200. INS 200 generates a programmableelectrical stimulation signal. INS 200 comprises a processor 201 with anoscillator 203, a calendar clock 205, a memory 207, a system resetmodule 209, a telemetry module 211, a recharge module 213, a powersource 215, a power management module 217, a therapy module 219, and atherapy measurement module 221. In non-rechargeable versions of INS 200,recharge module 213 can be omitted. Other versions of INS 200 caninclude additional modules such as a diagnostics module. All componentscan be configured on one or more Application Specific IntegratedCircuits (ASICs) except the power source. Also, all components areconnected to bi-directional data bus that is non-multiplexed withseparate address and data lines except oscillator 203, calendar clock205, and power source 215. Other embodiments may multiplex the addressand data lines. Processor 201 is synchronous and operates on low powersuch as a Motorola 68HC11 synthesized core operating with a compatibleinstruction set. Oscillator 203 operates at a frequency compatible withprocessor 201, associated components, and energy constraints such as inthe range from 100 KHz to 1.0 MHz. Calendar clock 205 counts the numberof seconds since a fixed date for date/time stamping of events and fortherapy control such as circadian rhythm linked therapies. Memory 207includes memory sufficient for operation of the INS such as volatileRandom Access Memory (RAM) for example Static RAM, nonvolatile Read OnlyMemory (ROM), Electrically Eraseable Programmable Read Only Memory(EEPROM) for example Flash EEPROM, and register arrays configured onASICs. Direct Memory Access (DMA) is available to selected modules suchas telemetry module 211, so telemetry module 211 can request control ofthe data bus and write data directly to memory bypassing processor 201.System reset module 209 controls operation of ASICs and modules duringpower-up of INS 200, so ASICs and modules registers can be loaded andbrought on-line in a stable condition. INS 200 can be configured in avariety of versions by removing modules not necessary for the particularconfiguration and by adding additional components or modules. Primarycell, non-rechargeable versions of INS 200 will not include some or allof the components in the recharge module. All components of INS 200 arecontained within or carried on a housing that is hermetically sealed andmanufactured from a biocompatible material such as titanium.Feedthroughs provide electrical connectivity through the housing whilemaintaining a hermetic seal, and the feedthroughs can be filtered toreduce incoming noise from sources such as cell phones.

[0045]FIG. 3 illustrates an example of a basic INS operation flowchart300. Operation begins with when processor 201 receives data from eithertelemetry 301 or from an internal source 303 in INS 200. At receivingdata step 305, received date is then stored in a memory location 307.The data 307 is processed by processor 201 in step 309 to identify thetype of data and can include further processing such as validating theintegrity of the data After data 307 is processed, a decision is madewhether to take an action in step 311. If no action is required, INS 201stands by to receive data. If an action is required, the action willinvolve one or more of the following modules or components: calendarclock 205, memory 207, telemetry 211, recharge 213, power management217, therapy 219, and therapy measurement 221. An example of an actionwould be to modify a programmed therapy. After the action is taken, adecision is made whether to prepare the action to be communicated instep 313, known as uplinked, to patient programmer 35 or consoleprogrammer 30 through telemetry module 211. If the action is uplinked,the action is recorded in patient programmer 35 or console programmer30. If the action is not uplinked, the action is recorded internallywithin INS 200.

[0046]FIG. 4 shows a block diagram of various components that may befound within telemetry module 211. Telemetry module 211 providesbi-directional communications between INS 200 and the programmers.Telemetry module 211 comprises a telemetry coil 401, a receiver 403, atransmitter 405, and a telemetry processor 407. Telemetry is conduced ata frequency in the range from about 150 KHz to 200 KHz using a medicaldevice protocol such as described in U.S. Pat. No. 5,752,977 entitled“Efficient High Data Rate Telemetry Format For Implanted Medical Device”issued on May 19, 1998 and having named inventors Grevious et al..Telemetry coil 401 can be located inside the housing or attached to theoutside of the housing, and telemetry coil 401 can also function as therecharge coil if operation of the coil is shared or multiplexed.Receiver 403 processes a digital pulse representing the Radio Frequency(RF) modulated signal, knows as a downlink, from a programmer.Transmitter 405 generates an RF modulated uplink signal from the digitalsignal generated by telemetry processor 407. Telemetry processor 407 maybe a state machine configured on an ASIC with the logic necessary todecode telemetry signal during reception, store data into RAM, andnotify processor 201 that data was received. Telemetry processor 407also provides the logic necessary during transmission to requestprocessor 201 to read data from RAM, encode the data for transmission,and notify the process that the data was transmitted. Telemetryprocessor 407 reduces some demands on processor 201 in order to saveenergy and enable processor 201 to be available for other functions.

[0047]FIG. 5 illustrates an example of a telemetry operation flowchart500. To begin telemetry, either the patient or the clinician usespatient programmer 35 or console programmer 30 and places the telemetryhead containing telemetry coil 401 near INS 200 or the ENS. In step 501,the RF telemetry signal is received through telemetry coil 401 andincludes a wake-up burst that signals telemetry processor 407 to preparetelemetry processor 407 to receive incoming telemetry signals. Telemetryprocessor 407 is configured to receive a particular telemetry protocolthat includes the type of telemetry modulation and the transmission rateof the incoming telemetry signal in step 503. Telemetry receiver 403demodulates the time base signal into digital pulses in step 505.Telemetry processor 407 converts the digital pulses into binary datathat is stored into memory. In step 509, processor 201 will then takewhatever action is directed by the received telemetry such as adjustingthe therapy. Telemetry signal transmission is initiated by processor 201requesting telemetry processor 407 to transmit data in step 551.Telemetry processor 407 is configured for the desired telemetry protocolthat includes the type of modulation and the speed for transmission instep 553. Telemetry processor 407 converts the binary data into a timebased digital pulses in step 555. Transmitter 405 modulates the digitalsignal into an RF signal that is then transmitted through telemetry coil401 to programmer 30 or 35 in step 559.

[0048]FIG. 6 shows a block diagram of various components that may befound within recharge module 213. Recharge module 213 providescontrolled power to the battery (contained in power source 215) forrecharging the battery and provides information to INS 200 aboutrecharging status. Recharge module 213 regulates the charging rate ofpower source 215 according to power source parameters and keeps thetemperature rise of INS 200 within acceptable limits so that thetemperature rise does not create an unsafe condition for the patient.INS 200 communicates charging status to the patient's charger (213), sothe patient charges at a level that prevents INS 200 from overheatingwhile charges power source 215 rapidly. Recharge module 213 comprises arecharge coil, an Alternating Current (AC) over-voltage protection unit601, an AC to DC converter 603, a recharge regulator 605, a rechargemeasurement unit 607, and a recharge regulator control 609. Rechargemodule 213 charges the battery by receiving a power transfer signal witha frequency of about 5.0 KHz to 10.0 KHz and converting the powertransfer signal into a regulated DC power that is used to charge thebattery. The recharge coil can be the same coil as telemetry coil 401 ifshared or multiplexed or the recharge coil can be a separate coil. ACover-voltage protection unit 601 can be a Zener diode that shunts highvoltage to ground. AC to DC converter 603 can be a standard rectifiercircuit. Recharge regulator 605 regulates the voltage received from ACto DC converter 603 to a level appropriate for charging the battery. Therecharge regulator control adjusts recharge regulator 605 in response torecharge measurements and a recharge program. The recharge program canvary based upon the type of device, type of battery, and condition ofthe battery. The recharge measurement block 607 measures current andvoltage at regulator 605. Based upon the recharge measurement, theregulation control can increase or decrease the power reaching powersource 215.

[0049]FIG. 7 illustrates an example of recharge module operationflowchart corresponding to recharge module 213. Recharging INS 200begins in the same manner as telemetry with either the patient or theclinician using patient programmer 35 or console programmer 30 andplacing the telemetry head containing the recharge coil near INS 200 orthe ENS. After the recharge signal is received in step 701, it isconverted to from AC to DC in step 703. The DC signal is regulated instep 707. Regulator output power is measured in step 707 and then fedback in step 705 in order to assist in controlling the regulator outputpower to an appropriate power level. Power source 215 is charged in step709, and the power source charge level is measured in step 711. Themeasured power source charge level also is fed back in step 705, soregulator 605 can control the regulator output to a level that isappropriate for power source 215. Once recharge module 213 fully chargespower source 215, recharge module 213 can be configured to function as apower source for INS 200 while power is still received.

[0050]FIG. 8 shows a block diagram of various components that may befound within power management module 217, and FIG. 9 illustrates anexample of a flowchart of power management module 217. Power managementmodule 217 provides a stable DC power source to INS 200 with voltagessufficient to operate INS 200 such as between about 1.5 VDC and 2.0 VDC.Power management module 217 includes a first DC to DC converter 801, asecond DC to DC converter 803, and power source measurement component805. One or more additional DC to DC converters can be added to thepower management module to provide additional voltage values for INS200. First DC to DC converter 801 and second DC to DC converter 803 canbe operational amplifiers configured for a gain necessary for thedesired output voltage. Power source measurement component 805 measuresthe power source and reports this measurement to processor 201, soprocessor 201 can determine information about power source 215. Ifprocessor 201 determines that power source 215 is inadequate for normaloperation, processor 201 can instruct power management module 217 toinitiate a controlled shutdown of INS 200.

[0051] INS power source 215 typically provides a voltage sufficient forpower management module 217 to supply power to INS 200 such as above 2.0VDC at a current in the range from about 5.0 mA to 30.0 mA for a timeperiod adequate for the intended therapy. INS power source 215 can be aphysical storage source such as a capacitor or super capacitor, or powersource 215 can be a chemical storage source such as a battery. The INSbattery can be a hermetically sealed rechargeable battery such as alithium ion (Li+) battery or a non-rechargeable battery such as alithium thionyl chloride battery. The ENS battery can be anon-hermetically sealed rechargeable battery such as nickel cadmium or anon-rechargeable battery such as an alkaline.

[0052]FIG. 10 shows a block diagram of various components that may befound within therapy module 219. Therapy module 219 generates aprogrammable stimulation signal that is transmitted through one or moreleads to electrical contacts implanted in the patient. Therapy module219 comprises a therapy controller (waveform controller) 1001, agenerator 1003, a regulator module 1005, and an electrical contactswitches unit 1007. Therapy controller 1001 can be a state machinehaving registers and a timer. Other embodiments of the invention mayutilize other types of processors such as an ASIC, a microprocessor, agate array, and discrete circuitry. Therapy controller 1001 controlsgenerator 1003 and regulator module 1005 to create a stimulation signal.(A waveform generator that forms the stimulation signal may comprisegenerator 1003 and regulator module 1005.) Generator 1003 assemblescapacitors that have been charged by power source 215 to generate a widevariety of voltages or currents. Regulator module 1005 includescurrent/voltage regulators that receive a therapy current or voltagefrom generator 1003 and shape the stimulation signal according totherapy controller 1001. Regulator module 1005 may include any number ofdevices or software components (active or passive) that maintains anoutput within a range of predetermined parameters such as current,voltage, etc. Electrical contact switches unit comprises solid stateswitches with low impedance such as Field Effect Transistor (FET)switches. The electrical contacts are carried on the distal end of alead and deliver the stimulation signal to the body through anelectrode. Additional switches can be added to provide a stimulationsignal to additional electrical contacts. In the embodiment, therapymodule 219 can deliver individual output pulses in the range from 0.0Volts to 15.0 Volts into a range from about 1.0 Ohm to 10.0 K Ohmsimpedance throughout its operating parameter range to any combination ofanodes and cathodes of up to eighteen electrical contacts for any givenstimulation signal. Other embodiments can support a different voltagerange, a different impedance range, or a different electrodearrangement.

[0053]FIG. 11 illustrates and example of operation with a flowchart oftherapy module 219. The therapy begins with the therapy controller 1001configuring the generator 1003 according to the therapy program toprovide appropriate voltage to regulator module 1005 in step 1101.Therapy controller 1001 also configures regulator module 1005 to producethe stimulation signal according to the therapy program in step 1103.Therapy controller 1001 also configures electrical contacts unit 1007 toso the stimulation signal is delivered to the electrical contactsspecified by the therapy program in step 1105. The stimulation signal isdelivered to the patient through electrodes in step 1107. After thestimulation signal is delivered to the patient, most therapies include atime delay in step 1109 before the next stimulation signal is delivered.

[0054]FIG. 12 shows a block diagram of various components that may befound within therapy measurement module 221. Therapy measurement module221 measures one or more therapy parameters at therapy module 219 todetermine whether the therapy is appropriate. Therapy measurement module221 includes a therapy voltage measurement component 1201, a therapycurrent measurement component 1203, and a therapy output measurementcomponent 1205. The therapy voltage measurements and therapy currentmeasurements are taken periodically to perform therapy calculations. Thetherapy output measurement is a measurement of the delivered therapythat is used for safety and other purposes.

[0055]FIG. 13 illustrates an example of an operation flowchart oftherapy measurement module 221. In step 1301, the therapy measurementoperation begins by processor 201 setting up parameters of the therapymeasurement to be taken (e.g. the specific stimulation signal tomeasure) and at which electrical contacts to perform the measurement.Before a therapy measurement is taken, a threshold determination is madewhether a therapy measurement is needed in step 1303. For sometherapies, a therapy measurement may not be taken. When a therapymeasurement is not taken, often a patient physiological measurement willbe performed and reported to processor 201 for action or storage inmemory in step 1305. When a therapy measurement is desired, the therapyis delivered in step 1307 and then the therapy measurement is performedin step 1309. The therapy measurement is reported to processor 201 foraction or storage in memory in step 1311. Examples of some actions thatmight be taken when the therapy measurement is reported include anadjustment to the therapy and a diary entry in memory that can beevaluated by the clinician at a later time.

[0056] Those skilled in the art will appreciate that the abovediscussion relating to the operation and components of the INS 14 serveas an example and that other embodiments may be utilized and still beconsidered to be within the scope of the present invention. For example,an ENS 25 may be utilized with the present invention.

[0057] Stimulation Engine. FIG. 14 shows a stimulation engine system1400 according to an embodiment of the present invention. Stimulationengine 1400 comprises therapy module 219 and therapy measurement block221. Therapy module 219 comprises generator control module 1003,waveform controller (therapy controller) 1001, regulators 1401, 1403,1405, and 1407, and electrode controller (electrical contact switchesunit) 1007. Regulators 1401-1407 receive an input voltage from acapacitor bank comprising capacitors 1451-1465. In the embodiment,capacitors 1451-1465 are associated as capacitor pairs such as describedin U.S. Pat. No. 5,948,004 entitled “Implantable Stimulation Having AnEfficient Output Generator” issued on Sep. 7, 1999 having namedinventors Weijand et al. Capacitors 1451-1465 are charged by a battery1467 during a recharging interval (during which a capacitor arrangementforms a charge configuration). If a capacitor pair is charged acrossbattery 1467 in parallel and subsequently discharged across a load inseries, the corresponding voltage (as provided to a regulator) is doubleof the voltage of battery 1467. If a capacitor pair is charged acrossbattery 1467 in series and subsequently discharged across the load inparallel, the corresponding voltage is one half the voltage of battery1467. The embodiment may utilize capacitor pairs both with a parallelconfiguration and with a series configuration in order to obtain adesired voltage level to a regulator. Moreover, other embodiments of theinvention can utilize other types of capacitor configurations (e.g.capacitor triplets to obtain one third of the battery voltage andcapacitor octets to obtain one eighth of the battery voltage) in orderto achieve a desired level of voltage granularity to a regulator. Thus,any fraction of the battery voltage can be obtained by a correspondingcapacitor configuration

[0058] In the embodiment, waveform controller 1001 (as instructed byprocessor 201) configures the capacitor bank through generator control1003 in order to provide the required voltage inputs (corresponding to1417-1423) to regulators 1401-1407, respectively (during which thecapacitor arrangement forms a stack configuration). Regulators 1401-1407are instructed to generate stimulation pulses (as illustrated in FIG.19) at time instances by waveform controller 1001 through control leads1409-1415, respectively. In the embodiment, a voltage drop across aregulator (e.g. 1401-1407) is determined by a digital to analogconverter (DAC) that is associated with the regulator and that iscontrolled by waveform controller 1001. In the embodiment, waveformcontroller 1001 can independently control as many as four regulators(1401-1407) in order to form four independent simulation channels,although other embodiments may support a different number of regulators.Each stimulation channel is coupled to electrode controller 1007 througha coupling capacitor (1471-1477). Each stimulation channel can becoupled to at least one of sixteen electrodes (E0-E15). Once again,variations of the embodiment may support different numbers ofelectrodes. An electrode may be either an anode or a cathode.

[0059] Therapy measurement block 221 monitors various components of thestimulation engine system 1400 for performance and diagnostic checks. Toassist with its monitoring function, therapy measurement block 221 hasassociated holding capacitors 1491 and 1493. Once again, variations ofthe embodiment may support different number of holding capacitors. Atleast one of the holding capacitors may be redundant in case the firstcapacitor has failed. As one example, therapy measurement block 221monitors the voltage across a regulator in order to detect whether thereis sufficient “headroom” (which is the voltage difference between theregulator's voltage input and voltage output). Some factors that mayalter the “headroom” include a change of the voltage of battery 1467 andchanging electrical characteristics of surrounding tissues (for example,caused by a movement in the placement of a lead). If a regulator doesnot have sufficient headroom, the regulator may not be able to regulatea stimulation pulse that has a constant amplitude over the duration ofthe pulse. Rather, the amplitude of the stimulation pulse may “droop.”In the embodiment, therapy measurement block 221 monitors input 1481 andinput 1485 to determine the input voltage and the output voltage ofregulator 1401. (In the embodiment, regulators 1403, 1405, and 1407 canbe similarly monitored.) Typically the voltage drop across regulatorshould be 0.3 volts or greater in order to achieve adequate regulation.For example, if therapy measurement block 221 determines that thevoltage drop across regulator 1401 is less than a minimum value, thentherapy measurement block 221 may notify processor 201 about regulator1401 experiencing an out-of-regulator condition. In such a case,processor 201 may instruct generator 1003 to associate another capacitorpair to the voltage input of regulator 1401 in order to increase theinput voltage. (It is assumed that redundant capacitor pairs areavailable.) Also, processor 201 may store the occurrence of theout-of-regulator and report the occurrence over a telemetry channelthrough telemetry module 211. The clinician may wish to recharge battery1467 in such a case.

[0060] If battery 1467 has been recharged after additional capacitorpairs have been configured to compensate for a previous out-of-regulatorcondition of regulator 1401, the voltage drop across a regulator may begreater than what is necessary to maintain adequate regulation. In sucha case, therapy measurement block 221 may remove a capacitor pair thatis associated with the voltage input of regulator 1401.

[0061] In another embodiment of the invention, therapy measurement block221 monitors the voltage of battery 1467. If the voltage of battery 1467is below a threshold value, therapy measurement block 221 reports thelow battery condition to processor 201. Consequently, processor 201 mayinstruct generator 1003 to configure capacitor pairs for the activeregulators (e.g. regulators 1401, 1403, 1405, and 1407). (It is assumedthat there are a sufficient number of capacitor pairs.). As discussedbelow, in yet another embodiment of the invention, therapy measurementblock 221 monitors various capacitive elements of the stimulation enginesystem 1400 for possible failure (e.g., holding capacitors 1491 and 1493and coupling capacitors 1471-1477).

[0062] Automatic Waveform Output Adjustment. FIG. 15A shows a logic flowdiagram 1500 for detecting an out-of-regulator condition. In step 1501,therapy measurement block 221 measures the voltage drop across aregulator (e.g. regulator 1401). In step 1503, therapy measurement block221 determines whether the voltage drop is less that a threshold value.If not, therapy measurement block monitors another regulator (e.g.regulator 1403) in step 1505. If so, then therapy measurement block 221informs INS processor 201 about the out-of-regulator condition in step1507. In step 1509, it is determined if a capacitor pair is available sothat the capacitor pair may be added to the associated capacitorconfiguration. If so, a capacitor pair is added and another regulator ismonitored.

[0063] Variations of the embodiment may detect a faulty capacitor of acapacitor pair. For example, if capacitor 1451 (C1) is shorted, theassociated voltage across capacitor 1451 is essentially zero.Consequently, the associated input voltage to a regulator is reduced,causing the voltage drop across the regulator to be reduced. With thelogic shown in FIG. 15A, another capacitor pair is configured in orderto compensate for capacitor 1451 shorting. Moreover, additional logicsteps can be included to detect a faulty capacitor and removing thefaulty capacitor from service. In a variation of the embodiment, acapacitor pair is removed from the capacitor arrangement and anothercapacitor pair is added. If the voltage drop across the regulator isconsequently within limits, the capacitor pair that was removed from theconfiguration is assumed to have a faulty capacitor. If a sparecapacitor pair is not available, processor 201 may be notified so thatprogrammer 30 or 35 can be alerted over the telemetry channel. Inanother embodiment, processor 201 may instruct the INS to shutdown inorder to deactivate the generation of a stimulation waveform that is notwith an acceptable range.

[0064] The embodiment may be used to detect other failure mechanisms.For example, rather than reconfiguring the capacitor configuration, anoriginal regulator can be replaced with a spare regulator. If a voltagedrop across the spare regulator is within an acceptable range, then theoriginal regulator is determined to be faulty. However, if it isdetermined that the original regulator is not faulty, the capacitorarrangement (comprising C1451-1465) can be tested. In one embodiment,the capacitors of the capacitor arrangement can be charged to a knownvoltage, such as the measured battery voltage, and the voltages acrossthe capacitors can be measured by therapy measurement block 221. If avoltage is low across a capacitor, the capacitor may be determined to befaulty. In such a case the capacitor may be replaced with a redundantcapacitor.

[0065]FIG. 15B shows an electrical configuration corresponding toregulators 1401, 1403, 1405, and 1407. The electrical configurationcomprises an amplifier 1553 in which an output 1557 feeds into anegative input and a programmed input voltage 1555 feeds into a positiveinput of amplifier 1553. Thus, amplifier 1553 is configured as a voltagefollower amplifier (i.e. output 1557 should approximately equalprogrammed input voltage 1555 if the circuitry is operating properly).Amplifier 1553 receives a power supply voltage from a capacitorarrangement 1551 through a reg top 1559 and a reg bottom 1561.

[0066] The embodiment corresponding to FIG. 15A measures a voltage dropacross a regulator (e.g. 1401, 1403, 1405, or 1407). In FIG. 15B, thevoltage drop across the regulator corresponds to a voltage differencebetween reg top 1559 and output 1557. Moreover, other embodiments of theinvention may utilize other electrical measurements in order todetermine an out-of-regulator condition. In one embodiment, if output1557 does not approximately equal programmed input voltage 1555, therapymeasurement block 221 may determine the occurrence of anout-of-regulator condition. In another embodiment, output 1557 (asmeasured by therapy measurement block 221) is compared with an expectedoutput voltage. In the embodiment, processor 201 is cognizant of theconfiguration of capacitor arrangement 1551 and the battery voltage.Processor 201 may use electrical formulae that correspond to the knownconfiguration in order to determine the expected output voltage. Asufficiently large difference between output 1557 and the expectedoutput voltage is indicative of an out-of-regulator condition. Inanother embodiment, an out-of-regulator condition is detected when thevoltage difference between reg top 1559 and reg bottom 1561(corresponding to an input signal to regulator 1401, 1403, 1405, or1407) is less than programmed input voltage 1555.

[0067] Detection and Correction of Possible Failure of CouplingCapacitor. In the embodiment, a coupling capacitor (e.g. 1471, 1473,1475, and 1477) is used to transfer charge to an electrode. Theaccumulated voltage across the coupling capacitor is a measure of thecharge that is transferred to the electrode. Moreover, the value of thecoupling capacitor determines the maximum charge that can be transferredto the electrode for a given stimulation voltage. However, the couplingcapacitor may fail in which the coupling capacitor becomes shorted. Insuch a case, the coupling capacitor becomes unable to limit excesscharge. In order to detect a shorted condition, therapy measurementblock 221 monitors the voltage drop across the coupling capacitor (e.g.capacitor 1471 which corresponds to regulator 1401). Inputs 1481 and1483 enable therapy measurement block 221 to monitor the voltage dropacross coupling capacitor 1471. Similar inputs are provided for eachother coupling capacitor (1473, 1475, and 1477) in circuit. A voltagedrop greater than or less than a prescribed range may be indicative of apossible failure in the coupling capacitor 1471.

[0068] Once the system detects a failed coupling capacitor, it may takeany number of corrective actions including, but not limited to, performa corrective recharge to compensate for the failure, replacing thefailed capacitor with another capacitor, notifying the implantablemedical device or the physician programmer, and/or shutting down theimplantable medical device. FIG. 16 shows a logic flow diagram 1600 ofone embodiment for detecting a faulty coupling capacitor and takingcorrective action. In step 1601, therapy measurement block 221 measuresthe voltage across the coupling capacitor (e.g. coupling capacitor1471). Although a voltage drop measurement across the coupling capacitoris made, any measurement providing charge information would suffice todetermine whether the capacitor has failed including, but not limitedto, energy information going in and out of the capacitive element, andcurrent information going in and out of the capacitive element. In step1603, if it is determined that the voltage drop is less than apredefined threshold, it is assumed that the coupling capacitor hasmalfunctioned and corrective action should be taken. Otherwise, step1605 is executed and another coupling capacitor is monitored by therapymeasurement block 221.

[0069] In step 1607, corrective action is taken by removing from servicethe coupling capacitor (e.g. coupling capacitor 1471) and its associatedregulator (e.g. 1401) and notifying the INS processor 201. In step 1609,logic 1600 determines if a spare capacitor/regulator pair can beconfigured in order to assume the functionality of the faulty capacitor.In either case, the INS processor 201 may be notified. The INS processor201 may then notify the clinician (i.e., the physician programmer 30)about the condition through the telemetry channel. If a spare regulatoris available, the spare regulator is configured in step 1613 to assumethe functionality of the regulator that was removed. INS processor 201is informed in step 1615. Step 1617 is executed, and another couplingcapacitor is monitored. In other embodiments, other forms of correctiveaction may be taken. For example, the system can provide a chargebalance pulse in an amount to compensate for the capacitive elementbeing outside the predefined threshold. The charge balance pulse can becalculated by determining charge going in and going out of the couplingcapacitor. For example, if the stimulation pulse is at a constantcurrent, the system can determine the current amount and duration. Thecharge balance pulse can then be in an amount that zeros out thedifference in the charges going in and going out of the couplingcapacitor. In another example, the system can just notify the INSprocessor 201 and physician programmer 30 or it can just simply shutitself down from operation.

[0070] Other embodiments of the invention may monitor the couplingcapacitor (e.g. coupling capacitor 1471) in order to detect whether thecoupling capacitor becomes open. In such a case, the voltage drop acrossthe coupling capacitor may exceed a predefined threshold. In this case,even the associated regulator/capacitor pair may become ineffective inthe treatment of the patient. Therapy measurement block 221 maytherefore remove the regulator/capacitor pair and configure a spareregulator.

[0071] In yet other embodiments, therapy measurement block 221 maymeasure other elements other than capacitive elements including, but notlimited to, holding capacitors 1491 and 1493. In one exemplaryembodiment, therapy measurement block 221 measures the voltage of thebattery using one of the holding capacitors 1491 or 1493. After acertain time period (e.g., several seconds or several minutes), therapymeasurement block 221 re-measures the voltage of the battery using thesame holding capacitor 1491 or 1493. Under proper operation of theholding capacitor 1491, the two voltage measurements should be roughlythe same. If the two voltage measurements vary by more than apredetermined threshold, however, there is likely a failure in theholding capacitor. Alternatively, if the original voltage measurement ofbattery is outside a predefined range, it may be indicative of a failedcapacitor. For example, if the original voltage measurement of batteryis be less than 2V, then it is likely that the holding capacitor hasfailed. This is the case since if the battery voltage had reached 2V,the circuitry would have already been shut down for purposes ofconserving battery resources. In another alternative, if the holdingcapacitor is open circuited, the therapy measurement block 221 wouldhave been unable to take the initial battery voltage measurement. Oncethe system determines a possible failure of the holding capacitor, itmay then take appropriate action as discussed above (e.g., replacingholding capacitor with redundant capacitor, notifying the implantablemedical device or physician programmer of capacitor failure, etc.).

[0072] Regulator Improvements. FIG. 17 shows a first configuration for aset of regulators comprising regulators 1401, 1403, 1405, and 1407according to an embodiment of the present invention. The configurationshown in FIG. 17 may be used to generate a Pulse Width “A” pulse (pwa)1923 that is shown in FIG. 19. Other embodiments may support a differentnumber of regulators in order to generate a different numbers ofcorresponding waveforms. Capacitors 1451, 1453, 1455, 1457, 1459, 1461,1463, and 1465 have been charged by battery 1467 so that capacitors 1459and 1461 have a 1.5 volt potential and capacitors 1451, 1453, 1455,1457, 1463, and 1465 have a 3.0 volt potential. In order to provide a3.0 volt input to regulator 1403, a 4.5 volt input to regulator 1407, a7.5 volt input to regulator 1405, and a 13.5 volt input to regulator1401, a voltage reference 1711 is configured with respect to BPLUS ofbattery 1467. Waveform controller 1101 configures the capacitors1451-1465 and the voltage reference through generator control 1003. Theoutput of regulator 1403 is connected to anode 1703; the output ofregulator 1407 is connected to anode 1707; the output of regulator 1405is connected to anode 1705; the output of regulator 1401 is connected toanode 1701; and voltage reference 1711 is connected to cathode 1709.

[0073]FIG. 18 shows a second configuration for a set of regulatorscomprising regulators 1401, 1403, 1405, and 1407 according to anembodiment of the present invention. The configuration shown in FIG. 18may be used to generate a pulse width “B” pulse (pwb) 1915 that is shownin FIG. 19. Capacitors 1451-1465 have the same voltage potential asshown in FIG. 17. However, waveform controller 1001 configures a voltagereference 1811 to be the negative side of capacitor 1451 so that theinput voltage to each regulator (1407, 1403, 1405, and 1401) has anegative polarity rather than a positive polarity. As in theconfiguration shown in FIG. 17, cathode 1709 is connected to the voltagereference. Consequently, the voltage outputs of regulators 1407, 1403,1405, and 1401 have a negative polarity. Waveform controller 1001 alsoconfigures capacitors 1451-1465 so that capacitors 1451 and 1453 arebetween voltage reference 1811 and the input of regulators 1407 and1403, capacitors 1451, 1453, 1455, 1457 are between voltage reference1811 and the input of regulator 1405, and capacitors 1451, 1453, 1455,1457, 1459, 1461, 1463, and 1465 are between voltage reference 1811 andthe input of regulator 1401.

[0074] Table 1 compares the voltage outputs of regulators 1401, 1403,1405, and 1407 in FIGS. 17 and 18. TABLE 1 Comparison of RegulatorOutput Voltages for pwa and pwb Configurations Pulse Width A Pulse WidthB Configuration Configuration Anode 1701 12 volts  −11 volts Anode 17032 volts −5 volts Anode 1705 6 volts −6 volts Anode 1707 3 volts −1.5volts

[0075] With regulators 1401, 1403, 1405, and 1407 having a capability ofgenerating negative voltage, the risk of a charge accumulation that maydamage surrounding tissue around stimulated electrodes is reduced. Therequired amplitude of a stimulation pulse pwa 1923 (as shown in FIG. 19)varies with the type of therapy.

[0076] With a therapy pulse (e.g. pwa 1923) that is delivered to thetissue, it may be necessary to retract an equal amount of charge fromthe same tissue after the therapy pulse is completed. This retraction ofcharge is typically done in the form of a secondary pulse, or rechargepulse, which causes an equal amount of charge to flow in the oppositedirection of the original therapy pulse. If the amount of charge in thesecondary pulse does not equal the amount of charge in the therapypulse, charge will accumulate on the electrode surface, and the chemicalreactions at the electrode-tissue interface will not remain balanced,which can cause tissue and electrode damage. For example, theaccumulated charge may be accompanied by electrolysis, thus causinghydrogen, oxygen and hydroxyl ions to form. As a result, the pH level ofthe immediate layer of fluid in the proximity of the electrode maydeviate from its norm. PH variations may oscillate between pH 4 and pH10 within a few microns of the electrode. Also, charge accumulation maycause dissolution of the electrode (e.g. platinum), resulting in leadcorrosion and possible damage to tissue that encounters the resultingchemical migration. Thus, the reduction of the net charge thataccumulates in the region of the treatment reduces the possibility ofaccompanying tissue damage and electrode damage.

[0077] As will be discussed in the context of FIG. 19, pwb pulse 1925may have a negative polarity (as supported by the regulatorconfiguration in FIG. 18). The negative charge that accumulates in thesurrounding tissue during pwb pulse 1925 counterpoises the positivecharge that accumulates during pwa pulse 1923.

[0078] If the electrical characteristics between a stimulated electrodepair can be modeled as an equivalent circuit having a capacitor, thecharge accumulated during pwa interval 1909 may be counterpoised by thecharge accumulated during pwb interval 1915 if the product (amplitude ofpwa 1923)*(interval of pwa 1909) approximately equals the product(amplitude of pwb 1925)*(interval of pwb 1915) when the polarities ofpwa pulse 1923 and pwb pulse 1925 are opposite of each other.

[0079] Other embodiments of the invention may generate positive andnegative current waveforms by converting a voltage pulse to a currentpulse, in which the output from the regulator is driven through aresistance in the regulator.

[0080] Recharge Delay and Second Pulse Generation. FIG. 19 showsstimulation waveform 1901 according to an embodiment of the presentinvention. FIG. 19 shows waveform 1901 spanning a rate period interval1902. Waveform 1901 may repeat or may change waveform characteristics(corresponding to changing a waveform parameter) during a next rateperiod interval. Stimulation waveform 1901 may be programmed in order tocustomize a therapeutical treatment to the needs of the patient. Aninitial delay (delay_1) interval 1905 commences with a rate triggerevent. The rate trigger event occurs at the beginning of each rateperiod interval. During a pulse width A (pwa) setup interval 1907,capacitors 1451-1465 are moved from a charge configuration to a stackconfiguration. A pulse width pwa interval 1909 commences upon thecompletion of interval 1907. During interval 1909, regulators 1401-1407apply voltage or current outputs to a set of electrodes (e.g. anodes)while corresponding electrodes (e.g. cathodes) are connected to astimulation voltage reference. In the embodiment, pwa interval 1909 isprogrammable from 0 to 655 msec with increments of 10 microseconds, inwhich an associated timer is a 16-bit timer.

[0081] A second delay (delay_2) interval 1911 may begin upon thecompletion of pwa interval 1909. During interval 1911, all electrodeconnections remain open. In the embodiment, second delay interval 1911is programmable from 0 to 655 msec with increments of 10 microseconds.

[0082] A pwb setup interval 1913 may begin upon the completion of seconddelay interval 1911. During interval 1913, capacitors 1451-1465 aremoved from a charge configuration to a stack configuration. A pwbinterval 1915 follows interval 1913. During pwb interval 1915,regulators 1401-1407 apply voltage or current outputs to the set ofelectrodes (e.g. anodes) while corresponding electrodes (e.g. cathodes)are connected to a stimulation voltage reference. In the embodiment, pwbinterval 1915 is programmable from 0 to 655 with increments of 10microseconds.

[0083] While the embodiment configures the stimulation pulse during pwainterval 1909 with a positive polarity and the stimulation pulse duringpwb interval 1915 with a negative polarity, other embodiments mayreverse the polarities. Moreover, other embodiments may configure bothpulses during intervals 1909 and 1915 to have the same polarity.

[0084] A third delay (delay_3) interval 1917 begins upon completion ofpwb interval 1915. During interval 1917, all electrodes connectionsremain open. In the embodiment, the third delay interval 1917 isprogrammable from 0 to 655 msec with increments of 10 microseconds.

[0085] A passive recharge interval 1919 is triggered by the completionthird delay interval 1917. During interval 1919, electrodes may beconnected to a system ground. In the embodiment, waveform controller1001 (through passive recharge control 1491) passively recharges theconnected electrodes in order to provide a charge balance in tissuesthat are adjacent to the connected electrodes. Passive recharging duringinterval 1919 may function to complete the recharging process that maybe associated with pwb interval 1915. In the embodiment, passiverecharge interval 1919 is programmable from 0 to 655 msec withincrements of 10 microseconds. A wait interval 1921 follows interval1919 in order to complete rate period interval 1902. In the embodiment,the rate period interval is programmable from 0 to 655 msec. In theembodiment, if the sum of the component intervals (1905, 1907, 1909,1911, 1913, 1915, 1917, 1919, and 1921) exceed the rate period interval,the rate period interval takes precedence over all components intervalsin the event of a conflict. For example, all waveform timers arereloaded and a new waveform may commence with the occurrence of ratetrigger event.

[0086] Pulses generated during pwa pulse interval 1909 and pwb interval1915 may be used to stimulate surrounding tissues or may be used toassist in charge balancing. The effects of charge balancing during apulse may be combined with charge balancing during passive rechargeinterval 1919 in order to obtain a desired charge balancing. (Rechargingmay provide charge balancing with active components or with passivecomponents or both.)

[0087] Other embodiments of the invention may initiate rate periodinterval 1902 with a different interval than delay_1 interval 1905. Forexample, other embodiments may define the beginning of rate periodinterval 1902 with passive recharge interval 1919. Moreover, with theembodiment or with other embodiments, any of the delay intervals(delay_1 interval 1905, delay_2 interval 1911, delay_3 interval 1917,wait interval 1921), pulse intervals (pwa interval 1909, pwb interval1915), setup intervals (pwa setup interval 1907, pwb setup interval1913), or passive recharge interval 1919 may be effectively deleted bysetting the corresponding value to approximately zero. Also, otherembodiments may utilize different time increments other than 10microseconds.

[0088]FIG. 19 also shows a second waveform 1903 that is formed duringthe formation of 1901. (In the embodiment, regulators 1401 and 1407 maybe utilized to form four waveforms.) Waveform 1903 is phased withwaveform 1901 (with each waveform having the same rate period interval).A pwa pulse 1927 (that is associated with waveform 1903) occurs afterthe completion of pwa pulse 1923 (that is associated with waveform1901). The clinician may stimulate a set of electrodes with waveform1901. The subsequent stimulation of the set of electrodes by waveform1903 may cause the firing of the neurons that may not be possible onlywith waveform 1901 or 1903 alone. In the embodiment, waveforms 1901(corresponding to regulator 1401) and 1903 (corresponding to regulator1403) may be applied to the same electrode or to two electrodes in closeproximity. In the embodiment, if regulators 1401 and 1405 are configuredto the same electrode, regulators 1401 and current amplitude waveforms.

[0089] In the embodiment, the rate period interval of waveforms 1901 and1903 are the same. However, other embodiments of the invention mayutilize different rates periods for different waveforms.

[0090]FIG. 20 shows a state diagram that a finite state machine 2000utilizes to form the waveforms as shown in FIG. 19 according to anembodiment of the present invention. A finite state machine may beassociated with each waveform that is generated by INS 200. In theembodiment, state machine 2000 is implemented with waveform controller1001. Waveform controller 1001, in accordance with state machine 2000,controls generator 1003, regulators 1401-1407, passive recharge control1491, and electrode control 1007 in order to generate stimulation pulsesin accordance with state machine 2000. Moreover, waveform controller1001 may obtain waveform parameters from processor 201. The clinicianmay alter a waveform parameter (e.g. pwa pulse duration 1909) by sendingan instruction over the telemetry channel through telemetry unit 211 toprocessor 201 in order to modify the waveform parameter. In thediscussion of FIG. 19, it is assumed that wave shaping (as will bediscussed in the context of FIG. 21) is not activated. In FIG. 20, astate delay_1 2001 corresponds to first delay interval 1905. Atransition 2051 initiates a state pwa setup 2003 upon the expiration ofinterval 1905. State 2003 corresponds to pwa setup interval 1913. Ifwave shaping is activated, states ws_1 2005, ws_2 2007, and ws_3 2009may be executed. (However, discussion of states 2005, 2007, and 2009 aredeferred until the discussion of FIG. 21.) A delay_2 state 2013 may beaccessed directly from state delay_1 2001 through transition 2050 if pwapulse is not generated during pwa interval 1909.

[0091] Assuming that wave shaping is not activated, a state pwa 2011 isexecuted upon the completion of pwa setup interval 1907 through atransition 2053. State pwa 2011 corresponds to interval pwa 1909 duringwhich pwa pulse 1923 is generated. Upon the completion of interval 1909,state delay_2 2013 is entered through a transition 2073. State 2013corresponds to delay_2 interval 1911. If pwb pulse is generated, a pwbsetup state 2015 is entered through transition 2077 upon the completionof delay_2 interval 1911. If pwb pulse 1925 is not generated, a delay_3state 2019 is entered through transition 2075 upon the completion ofdelay_2 interval 1911. State pwb setup 2015 corresponds to pwb setupinterval 1913 and state delay_3 state 2019 corresponds to delay_3interval 1917.

[0092] With the completion of pwb setup interval 1913, if pwb pulse 1925is to be generated, a pwb state 2017 is entered through transition 2079.The pwb state 2017 corresponds to pwb interval 1915 during which the pwbpulse 1925 is generated. Upon the completion of pwb interval 1915,delay_3 state 2019 is entered through transition 2081. Upon thecompletion of delay_3 interval 1917, finite state machine enters apassive recharge (pr) state 2021 through transition 2085 or a wait state2023 through transition 2083. The pr state 2021 may be circumvented ifrecharging during pwb 2017 state adequately eliminates a chargeaccumulation that occurs during pwa state 2003. The pr state 2001corresponds to passive charge interval 1919. Upon the completion ofpassive recharge interval 1919, state machine 2000 enters wait state2023, and remains in state 2023 until the completion of the rate periodinterval. State machine 2000 consequently repeats the execution ofstates 2001-2023.

[0093] Other embodiments of the invention may support a different numberof stimulation pulses (e.g. three, four, and so forth) during rateperiod interval 1902.

[0094] Wave Shaping. FIG. 21 shows a waveform 2101 in which stimulationpulse pwa 1923 is generated by wave shaping according to an embodimentof the present invention. Waveform 2101, as shown in FIG. 21, spans arate period interval 2102. Wave shaping of pwa 1923 corresponds to astate ws_1 2005, a state ws_2 2007, and a state ws_3 2009 (as shown infinite state machine 2000 in FIG. 20) and corresponds to a ws_1 duration2109, a ws_2 duration 2111, and a ws_3 duration 2113 in FIG. 21.Durations 2109,2111, and 2113 correspond to phases 1, 2, and 3 of pwapulse 1923. In the embodiment, pwa pulse 1923 is synthesized in order toadjust the therapeutical effectiveness of pwa pulse 1923. In theembodiment, without wave shaping, pwa pulse 1923 is essentially arectangular pulse (flat-topped) as illustrated in FIG. 19.

[0095] In the embodiment, pwa interval 1909 is subdivided into threephase intervals 2109, 2111, and 2113. During phase intervals 2109, 2111,or 2113, at least one parameter is associated with the stimulationwaveform. In the embodiment, a parameter may correspond tocharacteristics of the stimulation waveform (e.g. a desired amount ofrise during the phase) or may correspond to an electrode configurationin which the stimulation waveform is applied. In the embodiment, allother time intervals remain the same and all time intervals maintain thesame order of succession (e.g. pwb 1925 follows pwa 1923) as in the casewithout wave shaping. During each of the three phases (ws_1 2150, ws_22160, and ws_3 2170) of pwa pulse 1923, the output amplitude may berising, falling, or constant across a phase. (Other embodiments mayutilize a different number of phases. Typically, with a greater numberof phases, one can achieve a better approximation of a desired waveform.The desired waveform may correspond to any mathematical function,including a ramp, a sinusoidal wave, and so forth.) Each of the threephases is defined by a register containing an initial output amplitude,a register containing a final output amplitude, and a registercontaining a number of clock periods in which the amplitude outputremains constant across an incremental step. In the embodiment, a phaseduration (e.g. 2109, 2111, and 2113) is determined by:

(|final amplitude count−initial amplitude+1)*(number of clock periodsper step)

[0096] The output amplitude changes by one amplitude step afterremaining at the previous amplitude for a clock count equal to the valueof the clock periods per step as contained in a register. The outputamplitude range setting in a register determines a size of an amplitudestep. (In the embodiment, the step size may equal 10, 50, or 200millivolts.)

[0097] An example of wave shaping illustrates the embodiment as shown inFIG. 21. The step size is 500 millivolts for phases 2150 and 2160 and 1volt for phase 2170. The master waveform generator clock is 10microseconds. Durations 2109, 2111, and 2113 are each 400 microseconds.During duration 2109, the initial amplitude register contains 70 (46 ₁₆)and the final amplitude register contains 40 (28 ₁₆). The clock periodsper step is 10 or 100 microseconds (10*10 microseconds). During duration2109, waveform 2103 starts at 3.5 volts and descends 0.5 volts every 100microseconds until the amplitude value is 2.0 volts.

[0098] During duration 2111, the initial amplitude register contains 0and the final amplitude register contains 70 (46 ₁₆). The clock periodsper step is 10. During duration 2111, waveform 2105 starts at 0 voltsand ascends 0.5 volts every 100 microseconds until the amplitude valueis 3.5 volts. During duration 2113, the initial amplitude registercontains 30 (1E₁₆). The clock periods per step is 20 (corresponding to200 microseconds). During duration 2113, waveform 2107 starts at 1.5volts and ascends to 2.5 volts in one step.

[0099] Finite state machine 2000 (as shown in FIG. 20) supports waveshaping with ws_1 state 2005, ws_2 state 2007, and ws_3 state 2009. Withwave shaping enabled, state 2005, 2007, or 2009 is entered from pwasetup state 2003 through transitions 2057, 2055, and 2059, respectively.The pwa state is not executed when wave shaping is enabled. In theembodiment, the synthesis associated with any phase (2150, 2160, 2170)may be circumvented. For example, ws_1 state 2005 may enter ws_2 state2007 through transition 2061, may enter ws_3 state 2009 throughtransition 2063, or may enter delay_2 state 2013 through transition2065.

[0100] Other embodiments of the invention may support a different numberof phases than is utilized in the exemplary embodiment. Also, otherembodiments may utilize wave shaping for other portions of waveform 2101(e.g. a pwb pulse 2129).

[0101]FIG. 22 shows a first apparatus that supports wave shaping asshown in FIG. 19 according to an embodiment of the present invention.Output voltage V_(out) 2203 corresponds to phase 2150, 2160, or 2170. Adigital to analog converter (DAC) 2201 generates V_(out) 2203 inaccordance to a digital input 2209. Input 2209 is obtained from register2205. Register 2205 receives a digital input 2211 from waveformcontroller 1001. Input 2211 is stored in register 2205 when clocked byclk_step 2207, which occurs at a rate of updating phases 2150, 2160, or2170 (corresponding to a “step”). Waveform controller 1001 updatesdigital input 2211 in order to cause V_(out) 2203 to equal a desiredvalue during phases 2150, 2160, or 2170 in accordance with an initialoutput amplitude, a final output amplitude, an amplitude step size, anda step time duration parameters.

[0102] In a variation of the embodiment, DAC 2201 determines a voltagedrop across a regulator (e.g. 1401, 1403, 1405, or 1407). The value ofthe stimulation waveform (with a voltage amplitude) is approximately avoltage input to the regulator minus the voltage drop (as determined byDAC 2201). Consequently, digital input 2211 is determined by subtractingan approximate value of the stimulation waveform from the input voltageto the regulator.

[0103]FIG. 23 shows a second apparatus that supports wave shaping asshown in FIG. 19 according to an embodiment of the present invention. Anoutput V_(out) 2301 corresponds to phases 2150, 2160, and 2170 in FIG.21. V_(out) 2301 is the output of an analog adder 2303 having inputs2305 and 2307. Input 2305 is obtained from a gate 2309 in which a stepvoltage V_(i) 2311 is gated by a gate control 2313 in accordance with astep time duration. With apparatus 2300,

Vout=Vout+Vin

[0104]FIG. 24 shows a logic flow diagram 2400 representing a method forsupporting wave shaping according to an embodiment of the presentinvention. Step 2401 determines whether wave shaping is activated. Ifnot, process 2400 is exited in step 2403. In such a case, pwastimulation pulse 1923 is generated as an essentially flat pulse overtime duration 1909. If wave shaping for an i^(th) phase of the pwa pulseis activated, step 2405 is executed.

[0105] In step 2405, an initial output voltage V_(start), a final outputvoltage V_(final), a step size V_(i), a step duration t_(i), and a phasetime duration T_(i) are determined. In step 2407, V_(out) is equal toV_(start). Step 2409 determines if the step time duration t_(i) hasexpired. If so, V_(out) is incremented by the step size V_(i) in step2411. If V_(out) equals the final output voltage V_(final) in step 2413,the output voltage V_(out) remains constant until the end of the phaseduration T_(i) in step 2415. If V_(out) is not equal to the final outputvoltage V_(final) and the phase time duration T_(i) has not expired (asdetermined in step 2417), step 2409 is repeated in order to updateV_(out) for another step time duration t_(i).

[0106] Other embodiments of the invention may support wave shaping of acurrent amplitude of waveform 2101. In such cases, a voltage amplitudemay be converted into a current amplitude by driving a resistor that isassociated with a regulator (e.g. 1401, 1403, 1405, and 1407).

[0107] Simultaneous Delivery of a Plurality of Independent TherapyPrograms. FIG. 25 shows a stimulation arrangement that is associatedwith an implantable neuro stimulator according with prior art such asthat disclosed in U.S. Pat. No. 5,895,416. Lead 2501 comprises aplurality of electrodes including cathode 2503, cathode 2505, and anode2507. Anode 2507 provides a common reference for either a voltageamplitude pulse or a current amplitude pulse through cathodes 2503 and2505. Waveforms 2511 and 2513 are applied to cathodes 2503 and 2505,respectively. Waveform 2511 differs from waveform 2513 by amplitudescaling; however, component time durations are the same for waveform2511 and waveform 2513. Moreover, the waveforms serve to treat the sameneurological condition in a specific portion of the body.

[0108]FIG. 26 shows a stimulation electrode arrangement that isassociated with INS 200 according to an embodiment of the presentinvention. INS 200 stimulates leads 2601 and 2603. Lead 2601 compriseselectrodes 2605-2619, and lead 2603 comprises electrodes 2621-2635. Thebasic “unit” of therapy is a “therapy program” in which amplitudecharacteristics, pulse width, and electrode configuration are associatedwith a pulse train for treatment of a specific neurological conductionin a specific portion of the body. Multiple therapy programs maytherefore be used to either treat distinct neurological conditions ortreat the same neurological condition but in distinct areas of the body.The pulse train may comprise a plurality of pulses (voltage or currentamplitude) that are delivered essentially simultaneously to theelectrode configuration.

[0109] In FIG. 26, four therapy programs (program 2637, program 2639,program 2641, and program 2643) are configured and activated. In theembodiment, thirty two therapy programs may be defined in which one tofour therapy programs may be activated to form a therapy program set.(Other embodiments may support a different number of therapy programsand a different size of the therapy program set.)

[0110] Additional therapy programs (not directly accessible by thepatient) may be provided for any number of reasons including, forexample and without limitation, to treat neurological conditions indistinct parts of the body, to treat distinct neurological conditions,to support sub-threshold measurements, patient notification, andmeasurement functions. For example, a patient notification program isused to define an output pulse train for patient notification such assome type of patterned stimulation that can be discernable by thepatient. The patient notification program may be activated by a lowbattery (battery 1467) condition. A lead integrity measurement programdefines a pulse train to executing lead (e.g. 2601 and 2603) integritymeasurements.

[0111] In FIG. 26, the therapy program set comprises therapy programs2637 (program 1), 2639 (program 2), 2641 (program 3), and 2643 (program4). Each therapy program comprises four waveforms C1, C2, C3, and C4that are generated by regulators 1401, 1403, 1405, and 1407,respectively. Table 2 illustrates the configuration of the program setas shown in FIG. 26. Stimulation pulses are applied to cathodes2607-2617 of lead 2601 and to cathodes 2623-2633 of lead 2603, whileanodes 2605, 2619, 2621, and 2635 serve as common references. TABLE 2EXAMPLE OF THERAPY PROGRAM SET Lead 1 (2601) Lead 2 (2603) Electrode 1 23 4 5 6 1 2 3 4 5 6 program C1 C2 C3 C4 1 (2637) program C1 C2 C3 C4 2(2639) program C1 C2 C3 C4 3 (2641) program C1 C2 C3 C4 4 (2643)

[0112] With therapy program 2637 (program 1), stimulation pulses 2655,2657, 2651, and 2653 are applied to cathodes 2611, 2613, 2627, and 2629,respectively. With therapy program 2639 (program 2), stimulation pulses2665, 2667, 2661, and 2663 are applied to cathodes 2611, 2613, 2627, and2629, respectively. The pulse characteristics of a regulator (e.g. 1401,1403, 1405, 1407) may vary from one therapy program to another. Forexample, pulse 2655 and pulse 2665 are generated by regulator 1401;however, pulse 2655 and pulse 2665 may have different characteristics inorder to obtain a desired therapeutical effect.

[0113] With therapy program 2641 (program 3), stimulation pulses 2675,2677, 2671, and 2673 are applied to cathodes 2615,2617, 2631, and 2633,respectively. With therapy program 2643 (program 4), stimulation pulses2685, 2687, 2681, and 2683 are applied to cathodes 2607, 2609, 2623, and2625, respectively.

[0114] One skilled in the art will appreciate that the present inventioncan be practiced with embodiments other than those disclosed. Thedisclosed embodiments are presented for purposes of illustration and notlimitation, and the present invention is limited only by the claims thatfollow.

[0115] As can be appreciated by one skilled in the art, a computersystem with an associated computer-readable medium containinginstructions for controlling the computer system can be utilized toimplement the exemplary embodiments that are disclosed herein. Thecomputer system may include at least one computer such as amicroprocessor, digital signal processor, and associated peripheralelectronic circuitry.

[0116] Thus, embodiments of the VOLTAGE/CURRENT REGULATOR IMPROVEMENTSFOR AN IMPLANTABLE MEDICAL DEVICE are disclosed. One skilled in the artwill appreciate that the present invention can be practiced withembodiments other than those disclosed. The disclosed embodiments arepresented for purposes of illustration and not limitation, and thepresent invention is limited only by the claims that follow.

What is claimed is:
 1. An apparatus for generating a neurologicalstimulation waveform with an implantable medical device, comprising incombination: a capacitor arrangement coupled to an electrical referencethrough a first connection, wherein the capacitor arrangement comprisesa plurality of capacitors; a first regulator module coupled to thecapacitor arrangement through a second connection and coupled to a firstelectrode, wherein the second connection corresponds to a first value ofvoltage; and a switching array coupled to the capacitor arrangement inorder to reconfigure the capacitor arrangement with respect to theelectrical reference, wherein the second connection corresponds to asecond value of voltage.
 2. The apparatus of claim 1, wherein the firstregulator module comprises a voltage regulator.
 3. The apparatus ofclaim 1, wherein the first regulator module comprises a currentregulator.
 4. The apparatus of claim 1, wherein the capacitorarrangement comprises at least one capacitor pair.
 5. The apparatus ofclaim 1, wherein the capacitor arrangement comprises a collection ofcapacitors that corresponds to a fraction of a battery voltage.
 6. Theapparatus of claim 1, wherein the second value of voltage is differentthan the first value of voltage.
 7. The apparatus of claim 6, whereinthe second value of voltage has an opposite polarity of the first valueof voltage.
 8. The apparatus of claim 1, further comprising: a waveformcontroller coupled to the switching array in order to control theswitching array.
 9. The apparatus of claim 1, wherein the electricalreference is connected to a second electrode of the implantable medicaldevice.
 10. The apparatus of claim 1, further comprising: a secondregulator module coupled to the capacitor arrangement through a thirdconnection and coupled to a third electrode, wherein the thirdconnection is associated with a third value of voltage.
 11. Theapparatus of claim 10, wherein the third value of voltage is differentfrom the first value of voltage.
 12. A method for generating aneurological stimulation waveform with an implantable medical device,the steps comprising the steps of: (a) configuring a capacitorarrangement with respect to an electrical reference, wherein thecapacitor arrangement comprises a plurality of capacitors; (b)connecting a first regulator to the capacitor arrangement in order toobtain a first value of voltage; and (c) reconfiguring the capacitorarrangement with respect to the electrical reference in order to obtaina second value of voltage, the second value of voltage associated withthe first regulator.
 13. The method of claim 12, wherein the first valueof voltage has an opposite polarity of the second value of voltage. 14.The method of claim 12, further comprising the step of: (d) connecting asecond regulator to the capacitor arrangement in order to obtain a thirdvalue of voltage.
 15. The method of claim 14, further comprising thestep of: (e) reconfiguring the capacitor arrangement with respect to theelectrical reference in order to obtain a fourth value of voltage, thefourth value of voltage associated with the second regulator.
 16. Themethod of claim 14, wherein the third value of voltage is different fromthe first value of voltage.
 17. The method of claim 15, wherein thefourth value of voltage is different from the third value of voltage.18. A computer-readable medium containing instructions for generating aneurological stimulation waveform with an implantable medical device,comprising instructions that cause the implantable medical device toperform the steps of: (a) configuring a capacitor arrangement withrespect to an electrical reference, wherein the capacitor arrangementcomprises a plurality of capacitors; (b) connecting a regulator to thecapacitor arrangement in order to obtain a first value of voltage; and(c) reconfiguring the capacitor arrangement with respect to theelectrical reference in order to obtain a second value of voltage, thesecond value of voltage associated with the regulator.
 19. Animplantable medical device, comprising in combination: a telemetrymodule; a processor that communicates with a programmer through thetelemetry module in order to configure the implantable medical device; atherapy module connected to at least one electrode in order to provide aneurological stimulation waveform to a patient and connected to theprocessor in order to receive configuration information and commandsabout therapeutical treatment, the therapy module comprising: a waveformgenerator, comprising: a regulator; a capacitor arrangement connected toan input of the regulator; and a switching array coupled to thecapacitor arrangement in order to configure the capacitor arrangement,the capacitor arrangement comprising a plurality of capacitors; and awaveform controller coupled to the switching array in order to controlthe switching array, the waveform controller configured to perform thesteps of (a) configuring the capacitor arrangement with respect to anelectrical reference in order to obtain a first value of voltage; and(b) reconfiguring the capacitor arrangement with respect to theelectrical reference in order to obtain a second value of voltage, thesecond value of voltage having an opposite polarity as the first valueof voltage.